Hi Alexander,
The code that lets someone modify an existing image has an important and
undesirable side effect of making images mutable. Since we cache images
internally, they are treated as immutable so that if two unrelated
parties ask for an image that comes from a specific URL, we can give
them back the same object (with a bit of code internally to make sure
that each and both of them have permissions to access the specified
URL/filename/source). So, the first solution that adds a new method
onto Image that lets someone add a resolution variant after the fact is
not feasible. (Arguably, we could override and sabotage attempts to add
new variants, but that style of providing an API that is implemented in
a common case by blocking code is not very interesting.)
The version that provides an interface allows us to implement automatic
loading of resolution variants internally and expose that information in
a read-only fashion without making a cached Image object (or its
resolution variants) mutable - as long as we only ever provide immutable
collections populated by other immutable images. It can be combined
with an Image subclass variant that lets a developer specify their own
list of images, and potentially even add more images to that list on the
fly after the image is created (because it is not shared by a hidden
mechanism since they created it directly). We could probably add that
to BufferedImage since those are not shared, but we'd have to make sure
that shared "Toolkit images" don't subclass from BufferedImage or expose
that through their API - that's probably already true otherwise we'd
have provided a way for someone to scribble on a shared image.
I'll look into the second proposal (the interface variant) in a little
more detail, but I wanted to get this basic comment out there in advance
of more specific feedback...
...jim
On 1/22/2015 6:49 AM, Alexander Scherbatiy wrote:
Hi Phil,
I have prepared two versions of the proposed API:
I) Resolution variants are added directly to the Image:
http://cr.openjdk.java.net/~alexsch/8029339/list/webrev.00
II) MultiResolutionImage interface is used:
http://cr.openjdk.java.net/~alexsch/8029339/webrev.05
It could help to decide which way should be chosen for the the
multi-resolution image support.
Below are some comments:
1. High level goal:
Introduce an API that allows to create and handle an image with
resolution variants.
2. What is not subject of the provided API
- Scale naming convention for high-resolution images
- Providing pixel scale factor for the screen/window
3. Use cases
3.1 Loading and drawing high-resolution icons in IntelliJ IDEA
A high-resolution image is loaded from resources and stored in
JBHiDPIScaledImage class which is a subclass of the buffered image.
The high-resolution image is used to create a disabled icon in the
IconLoader.getDisabledIcon(icon) method.
https://github.com/JetBrains/intellij-community/blob/master/platform/util/src/com/intellij/openapi/util/IconLoader.java
3.2 Loading and drawing high-resolution icons in NetBeans
NetBeans does not have support for the high-resolution icons loading.
It loads an icon from the file system using
Toolkit.getDefaultToolkit().getImage(url) method or from resources
by ImageReader and store it in ToolTipImage class which is
subclass of the buffered image.
ImageUtilities.createDisabledIcon(icon) method creates a disabled
icon by applying RGBImageFilter to the icon.
http://hg.netbeans.org/main/file/97dcf49eb4a7/openide.util/src/org/openide/util/ImageUtilities.java
3.3 Loading system icons in JDK 1.8
JDK requests icons from the native system for system L&Fs and
applies filters for them.
See for example AquaUtils.generateLightenedImage() method:
http://hg.openjdk.java.net/jdk9/client/jdk/file/e6f48c4fad38/src/java.desktop/macosx/classes/com/apple/laf/AquaUtils.java
4. HiDPI support for Images on different OSes
4.1 Mac OS X
Cocoa API contains NSImage that allows to work with image
representations: add/remove/get all representations.
It picks up an image with necessary resolution based on the
screen backing store pixel scale factor and applied transforms.
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSImage_Class/Reference/Reference.html
4.2 Linux
GTK+ 3 API has gtkcssimagescaled lib (it seems that it is not
public/stable)
that parses the -gtk-scaled css property and draws a GtkCssImage
according to the given scale factor.
I have not found information about the HiDPI support in Xlib.
4.3 Windows
I have only found the tutorial that suggests to select and draw a
bitmap using the queried DPI
and scale the coordinates for drawing a rectangular frame
http://msdn.microsoft.com/en-us/library/dd464659%28v=vs.85%29.aspx
Windows also provides the horizontal and vertical DPI of the desktop
http://msdn.microsoft.com/en-us/library/windows/apps/dd371316
5. Pseudo API
Below are some ways which illustrates how multi-resolution images
can be created and used.
5.1 Resolution variants are stored directly in Image class.
To query a resolution variant it needs to compare the resolution
variant width/height
with the requested high-resolution size.
------------
public abstract class Image {
public void addResolutionVariant(Image image) {...}
public List<Image> getResolutionVariants() {...}
}
------------
// create a disabled image with resolution variants
Image disabledImage = getDisabledImage(image);
for (Image rv : image.getResolutionVariants()) {
disabledImage.addResolutionVariant(getDisabledImage(rv));
}
------------
This approach requires that all resolution variants have been
created even not of them are really used.
5.2 Resolution variants are stored in a separate object that
allows to create them by demand.
To query a resolution variant it needs to compare the resolution
variant scale factor
with the requested scale (that can include both screen DPI scale
and applied transforms).
------------
public abstract class Image {
public static interface ResolutionVariant {
Image getImage();
float getScaleFactor();
}
public void addResolutionVariant(ResolutionVariant
resolutionVariant) {...}
public List<ResolutionVariant> getResolutionVariants() {...}
}
------------
// create a disabled image with resolution variants
Image disabledImage = getDisabledImage(image);
for (Image.ResolutionVariant rv : image.getResolutionVariants()) {
disabledImage.addResolutionVariant(new Image.ResolutionVariant() {
public Image getImage() {
return getDisabledImage(rv.getImage());
}
public float getScaleFactor() {
return rv.getScaleFactor();
}
});
}
------------
It does not have problem if a predefined set of images is provided
(like image.png and im...@2x.png on the file system).
This does not cover cases where a resolution variant can be created
using the exact requested size (like loading icons from the native system).
A resolution variant can be queried based on a scale factor and
applied transforms.
5.3 The provided example allows to create a resolution variant
using the requested high-resolution image size.
------------
public interface MultiResolutionImage {
Image getResolutionVariant(float width, float height);
}
------------
// create a multi-resolution image
Image mrImage = new AbstractMultiResolutionImage() {
public Image getResolutionVariant(float width, float height) {
// create and return a resolution variant with exact
requested width/height size
}
protected Image getBaseImage() {
return baseImage;
}
};
------------
// create a disabled image with resolution variants
Image disabledImage = null;
if (image instanceof MultiResolutionImage) {
final MultiResolutionImage mrImage = (MultiResolutionImage) image;
disabledImage = new AbstractMultiResolutionImage(){
public Image getResolutionVariant(float width, float height) {
return
getDisabledImage(mrImage.getResolutionVariant(width, height));
}
protected Image getBaseImage() {
return getDisabledImage(mrImage);
}
};
} else {
disabledImage = getDisabledImage(image);
}
------------
Thanks,
Alexandr.
